It is known that titanium dioxide mixed oxide can be produced hydrolytically in the gaseous phase. Thus, published German Patent Application DE-A 9 52 891 describes a method of producing mixed oxides of aluminum and titanium or of titanium and silicon in which the temperature is maintained in the range between 250.degree. and 650.degree. C.
Published German Patent Application DE-A 29 31 810 (U.S. Pat. No. 4,297,143) describes a flame-hydrolytically produced silicon dioxide--titanium dioxide mixed oxide containing 99.9 to 91.1% by weight silicon dioxide and 0.1 to 9.9% by weight titanium dioxide.
Published German Patent Application DE-A 36 11 449 describes a flame-hydrolytically produced aluminum oxide titanium oxide mixed oxide containing 56% by weight aluminum oxide and 44% by weight titanium dioxide.